Wheelchair suspension

ABSTRACT

A wheelchair includes a frame, a rear caster coupled to the frame, a drive wheel coupled to the frame, a front caster, and a pivoting assembly. The pivoting assembly couples the front caster to the frame such that upward movement of the front caster relative to the frame causes the front caster to move toward the drive wheel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 12/330,554, filed Dec. 9, 2008, now U.S. Pat. No. 8,172,015, issued May 8, 2012, titled “Wheelchair Suspension”, which is a continuation of U.S. patent application Ser. No. 11/429,687, filed May 8, 2006, now U.S. Pat. No. 7,472,767, issued Jan. 6, 2009, which is a continuation of U.S. patent application Ser. No. 10/762,977, filed Jan. 22, 2004, now U.S. Pat. No. 7,055,634, issued Jun. 6, 2006, which is a continuation of U.S. patent application Ser. No. 09/974,348, filed Oct. 10, 2001, now U.S. Pat. No. 7,040,429, issued May 9, 2006, the disclosures of which are fully incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates generally to conveyances and, more particularly, to wheelchair suspensions.

BACKGROUND OF THE INVENTION

Wheelchairs are an important means of transportation for a significant portion of society. Whether manual or powered, wheelchairs provide an important degree of independence for those they assist. However, this degree of independence can be limited if the wheelchair is required to traverse obstacles such as, for example, curbs that are commonly present at sidewalks, driveways, and other paved surface interfaces.

In this regard, most wheelchairs have front and rear casters to stabilize the chair from tipping forward or backward and to ensure that the drive wheels are always in contact with the ground. One such wheelchair is disclosed in U.S. Pat. No. 5,435,404 to Garin. On such wheelchairs, the caster wheels are typically much smaller than the driving wheels and located both forward and rear of the drive wheels. Though this configuration provided the wheelchair with greater stability, it made it difficult for such wheelchairs to climb over obstacles such as, for example, curbs or the like, because the front casters could not be driven over the obstacle due to their small size and constant contact with the ground.

U.S. Pat. No. 5,964,473 to Degonda et al. describes a wheelchair having front and rear casters similar to Garin and a pair of additional forward lift wheels. The lift wheels are positioned off the ground and slightly forward of the front caster. Configured as such, the lift wheels first engage a curb and cause the wheelchair to tip backwards. As the wheelchair tips backwards, the front caster raises off the ground to a height so that it either clears the curb or can be driven over the curb.

U.S. Pat. No. 6,196,343 to Strautnieks also describes a wheelchair having front and rear casters. The front casters are each connected to a pivot arm that is pivotally attached to the sides of the wheelchair frame. Springs bias each pivot arm to limit the vertical movement thereof. So constructed, each front caster can undergo vertical movement when running over an obstacle.

SUMMARY OF THE INVENTION

The present invention relates to a wheelchair. The wheelchair includes a frame, a rear caster coupled to the frame, a drive wheel coupled to the frame, a front caster, and a pivoting assembly. The pivoting assembly couples the front caster to the frame such that upward movement of the front caster relative to the frame causes the front caster to move toward the drive wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to example the principles of this invention.

FIG. 1 is a perspective view of a wheelchair incorporating the suspension of the present invention.

FIG. 2 is an exploded perspective view of certain components of the wheelchair of FIG. 1.

FIG. 3 is an exploded detail view of certain components of a side frame assembly of the present invention.

FIG. 4 is a side elevational view of the side frame assembly under static conditions.

FIG. 5 is a side elevational view of the side frame assembly traversing an obstacle by ascending an obstacle.

FIG. 6 is a side elevational view of the side frame assembly traversing an obstacle by descending the obstacle.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT

The present invention provides a wheelchair and suspension for traversing obstacles and rough terrain. The present invention facilitates the traversing of obstacles and rough terrain by allowing for the vertical and lateral movement of one or more front caster assemblies coupled to the wheelchair.

Referring now to FIG. 1, a perspective view of a wheelchair 100 of the present invention is shown. Wheelchair 100 is preferably a mid-wheel drive or rear-wheel drive wheelchair. As shown, wheelchair 100 has a chair 102 having arm supports 104 and 106. A control device such as, for example, a joystick controller 108 is attached to the chair 102 for controlling any power-related aspects of wheelchair 100. Wheelchair 100 further has removable decorative shrouds 110 covering the wheelchair's suspension, drive, and control systems. Projecting forward from the shrouds 110 is footrest 112 for supporting the feet of the wheelchair's user.

Illustrated in FIG. 2 is an exploded perspective view of certain components of wheelchair 100. The suspension system has a sub-frame 200 for accommodating, among other things, removable batteries 226 and 228. Removably attached to sub-frame 200 are first and second side frame assemblies 202 and 204. Side frame assemblies 202 and 204 are removably attached to sub-frame 202 via interfaces preferably in the form of spring loaded hooks and latches. The spring loaded hooks preferably reside on sub-frame 200 with the corresponding latches residing on side-frame assemblies 202 and 204. In this manner, an individual can manually without the use of tools take apart wheelchair 100 for easy transportation in, for example, the trunk of a car or other large vehicle.

Each side frame assembly has at least one drive assembly having a motor drive 210 and 212 and a drive wheel 206 and 208. Each motor drive 210 and 212 preferably has either a motor/gear box combination or a brushless, gearless motor. Each side frame assembly further has at least one front caster assembly 218 and 220 coupled thereto via pivoting assemblies 214 and 216. At least one rear caster assembly 222 and 224 are also provided for each side frame assembly. Each of the side frame assemblies are identical in construction and, hence, the present discussion will focus on describing side frame assembly 202 with the understanding that such discussion is equally applicable to side frame assembly 204.

Referring now to FIG. 3, an exploded detailed perspective of certain components of side frame simply 202 is shown. In this regard, side frame assembly 202 has a side frame member 301 having sub-members 302, 304, 306, and 318. These side frame sub-members are preferably tubular (i.e., circular, oval, or rectangular in cross-section) and formed and welded together has shown. Pivoting assembly 214 has a first pivoting linkage 319 defined by sub-linkages 320, 322, 324, and 326. These sub-linkages are also preferably tubular in configuration, as described above, and formed and welded together as shown. Sub-linkage 326 has a motor drive assembly mounting bracket 328 attached thereto. A second pivoting linkage 334 is also provided. As shown in FIG. 3, the overall length of the first pivoting linkage 319 is greater than the overall length of the second pivoting linkage 334. As will be presently described, this configuration facilitates, for example, the dual functions of lifting and retracting the front caster assembly 335 away from the obstacle to be traversed and inward toward the wheelchair.

The first pivoting linkage 319 is pivotally coupled to side frame member 301 via tubular stud or extension 308. The second pivoting linkage 334 is pivotally coupled to side through member 301 via tubular stud or extension 312. A compression plate 332 is provided for additional stability and is coupled to side frame member 301 via tubular studs or extensions 308 and 312 and pivot stop member 310.

Resilient extension springs 344 and 346 are provided between side frame member 301 and first pivoting linkage 319. In this regard, spring 344 has a first connection to frame member 301 via bracket 314 and a second connection to first pivoting linkage 319 via bracket 330. Spring 346 has a first connection to frame member 301 via bracket 316 and a second connection to first pivoting linkage 319 via bracket 348. As will be described in more detail, extension springs 344 and 346 are connected to first pivoting linkage 319 on either side of the linkages pivotal connection to side frame member 301 and provide a unidirectional bias force around the first pivoting linkage 319 pivotal coupling to side frame member 301. Alternatively, resilient elastomeric members can be integrated into the pivotal coupling between first pivoting linkage 319 and side frame member 301. Similarly, resilient elastomeric members can be integrated into the pivotal coupling between second pivoting linkage 334 and side frame member 301. Such resilient elastomeric members can be “Rosta”-type bearings or other similar structures.

A front caster assembly 335 is pivotally coupled to each of the first and second pivoting linkages 319 and 334. In this regard, front caster assembly 335 has an integral head tube/bracket 336 for receiving a caster fork 337 and making the aforementioned pivotal couplings to linkages 319 and 334. These pivotal couplings to linkages 319 and 334 are facilitated by first and second holes 338 and 340 in head tube/bracket 336 and corresponding tubular formations in first and second pivoting linkages 319 and 334. A rear caster is attached to side frame assembly 301 via rear caster fork 342, which is received in sub-frame member 318.

Configured as such, first and second pivoting linkages 319 and 334 pivot with respect to side frame member 301. Moreover, front caster assembly 335 undergoes spatial displacement with the pivotal movement of first and second pivoting linkages 319 and 334. The rear caster wheel and fork 342 are generally not affected by the pivotal movement of first and second pivoting linkages 319 and 334.

Referring now to FIG. 4, an outer side elevational view of side frame assembly 202 is shown under static conditions (i.e., the wheelchair is standing still or neither accelerating or decelerating). Drive wheel 206 is only partially shown so to not obscure the relevant components of side frame assembly 202. In this state, all wheels including the drive wheels and front and rear caster wheels are in contact and maintain contact with the ground or other riding surface.

Referring now to FIG. 5, an inner side elevational view of side frame assembly 202 is shown as the wheelchair traverses an elevated obstacle. The component displacement shown in FIG. 5 normally occurs when the wheelchair is quickly accelerated forward to traverse an obstacle such as curb 500. For purposes of the present discussion, the pivotal coupling between first pivoting linkage 319 and side frame member 301 is designated by pivot P1. Similarly, the pivotal coupling between the second pivoting linkage 334 and side frame member 301 is designated by pivot P2. In relationship to each other, it can be seen that pivot P2 is below and laterally offset from pivot P1 in a direction toward the front caster. In other words, pivot P2 is laterally closer to front caster assembly 335 than is pivot P1. In combination with the respective overall lengths of first and second pivoting linkages 319 and 334, this configuration provides the dual functions of lifting and retracting the front caster assembly 335 away from the obstacle to be traversed and inward toward the wheelchair.

In this regard, when the wheelchair is accelerated forward by a high rate, the resulting moment arm generated by the drive wheel 206 will exceed the resultant moment arm generated by springs 344 and 346. This causes first pivoting linkage 319 to pivot or rotate in a clockwise direction about pivot P1 thereby raising front caster assembly 335. This motion also causes second pivoting linkage 334 to undergo pivotal motion. The resulting effect of second pivoting linkage 334 motion is to cause front caster assembly 335 to pivot about its pivotal coupling 338 to first pivoting linkage 319. This pivotal movement causes front caster assembly 335 to be drawn inward toward the wheelchair itself and away from the obstacle 500 being traversed. The maximum amount of pivotal movement is limited by stop 310, which physically engages side frame member 301 sub-linkage 320. The same effect described above is achieved should side frame assembly 202 be driven directly over obstacle 500. Once the resultant movement arm generated by drive wheel 206 is less than the resultant movement arm generated by springs 344 and 346 with respect to pivot P1 front caster assembly 335 is lowered.

Referring now to FIG. 6, an inner side elevational view of side frame assembly 202 is shown as the wheelchair traverses descends an obstacle 600. In this regard, the resultant moment arm generated by springs 344 and 346 is greater than any other moment arm around pivot P1. This causes first pivoting linkage 319 to rotate counter-clockwise and to lower the front caster assembly 335 on the lower supporting or riding surface. In this regard, the respective position of pivot P2 and the overall length of second pivoting linkage 334 compared to the position of pivot P1 and the overall length of first pivoting linkage 319 provide for front caster assembly 335 to descend to the lower supporting surface. Concurrently therewith, the pivotal motion of second pivoting linkage 334 causes front caster assembly 335 to pivot about its pivotal coupling 338 to first pivoting linkage 319. This motion causes front caster assembly 335 to extend forward. The combined effect of lowering and extending front caster assembly 335 provide the wheelchair with greater stability when descending a obstacle because the wheelchair is sooner and longer in contact with the differing elevations that represent the obstacle. The maximum pivotal movement is once again limited by stop 310, which physically engages side frame member 301 sub-linkage 322 in this scenario.

Hence, the present invention facilitates the traversing of obstacles and rough terrain by allowing for the vertical and lateral movement of one or more front caster assemblies.

While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, a plurality of casters can be used instead of one caster, the casters can be coupled to the pivot arms via shock absorbing fork assemblies, and the specific locations of the pivotal couplings can be modified so long as the above-described overall relationships are maintained. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures can be made from such details without departing from the spirit or scope of the applicant's general inventive concept. 

The invention claimed is:
 1. A wheelchair suspension comprising: a frame; at least one rear caster coupled to the frame; a drive assembly coupled to the frame; a pivoting assembly mounting a front caster to the frame, the pivoting assembly comprising: a front caster assembly having a head tube rotatably receiving a caster fork that rotatably supports a caster wheel; an upper link pivotally mounted to the front caster assembly at a first upper pivot axis and to the frame at a second upper pivot axis; a lower link pivotally mounted to the front caster assembly at a first lower pivot axis and to the frame at a second lower pivot axis; wherein the distance between the first upper pivot axis and the second upper pivot axis is different than the distance between the first lower pivot axis and the second lower pivot axis; wherein the second lower pivot axis and the second upper pivot axis are substantially offset on the frame such that when the wheelchair suspension is on a level support surface a horizontal distance between the second lower pivot axis and the second upper pivot axis is greater than one-half a vertical distance between the second lower pivot axis and the second upper pivot axis.
 2. The wheelchair suspension of claim 1 wherein the distance between the first upper pivot axis and the second upper pivot axis is greater than the distance between the first lower pivot axis and the second lower pivot axis.
 3. The wheelchair suspension of claim 1 wherein the drive assembly is coupled to the pivoting assembly.
 4. The wheelchair suspension of claim 1 wherein upward pivotal movement of the first and second pivot linkages causes the caster wheel to move toward the frame.
 5. The wheelchair suspension of claim 1 further comprising a spring attached to each suspension assembly, such that the spring biases the front caster wheel into engagement with the ground.
 6. A wheelchair suspension comprising: a frame; a rear caster coupled to the frame; a drive wheel; a front caster assembly having a head tube rotatably receiving a caster fork that rotatably supports a caster wheel; a pivoting assembly that couples the front caster assembly to the frame at pivot axes such that upward movement of the front caster head tube relative to the frame causes the front caster wheel to move laterally toward the frame; and wherein a drive axle of the drive wheel is below said pivot axes when the wheelchair is disposed on a level support surface.
 7. The wheelchair suspension of claim 6 further comprising a spring coupled to the pivoting assembly such that the front caster wheel is biased into engagement with the ground.
 8. The wheelchair suspension of claim 6 wherein the pivoting assembly comprises first and second pivot linkages pivotally coupled to the frame and the front caster assembly.
 9. The wheelchair suspension of claim 6 wherein the drive wheel is coupled to the pivoting assembly.
 10. A wheelchair suspension comprising: a frame; a rear caster coupled to the frame; a drive wheel; a front caster assembly having a head tube rotatably receiving a caster fork that rotatably supports a caster wheel; and a pivoting means that couples the front caster assembly to the frame at a first pivot axis and a second pivot axis such that upward movement of the front caster assembly relative to the frame causes the front caster wheel to move toward the frame; wherein the first pivot axis and the second pivot axis are substantially offset on the frame such that when the wheelchair suspension is on a level support surface a horizontal distance between the first pivot axis and the second pivot axis is greater than one-half a vertical distance between the first pivot axis and the second pivot axis.
 11. The wheelchair suspension of claim 10 wherein the drive wheel is coupled to the pivoting assembly.
 12. The wheelchair suspension of claim 10 further comprising a spring coupled to the pivoting assembly such that the front caster wheel is biased into engagement with the ground.
 13. A wheelchair suspension comprising: a frame; at least one rear caster coupled to the frame; a drive wheel coupled to the frame; a pivoting assembly mounting a front caster to the frame, the pivoting assembly comprising: a front caster assembly having a head tube rotatably receiving a caster fork that rotatably supports a caster wheel; an upper linkage pivotally mounted to the front caster assembly and to the frame at respective upper pivot axes; a lower linkage pivotally mounted to the front caster assembly and to the frame at respective lower pivot axes; wherein the distance between the upper pivot axes is different than the distance between the lower pivot axes, such that upward movement of the front caster head tube relative to the frame causes the front caster wheel to move laterally toward the frame; and wherein a drive axle of the drive wheel is below the lower pivot axes when the wheelchair is disposed on a level support surface.
 14. The wheelchair suspension of claim 13 wherein the drive wheel is coupled to the pivoting assembly.
 15. The wheelchair suspension of claim 13, wherein the distance between the upper pivot axes is greater than the distance between the lower pivot axes.
 16. The wheelchair suspension of claim 13 further comprising a spring attached to the pivoting assembly such that the spring biases the front caster wheel into engagement with the ground.
 17. A wheelchair comprising: a frame member; a drive assembly; at least one rear caster coupled to the frame member; at least one pivoting assembly having: a first linkage pivotally coupled to the frame member at an upper pivot axis, wherein the upper pivot axis is disposed between a forward portion and a rearward portion of the first linkage; and a second linkage pivotally coupled to the frame member; and a third linkage pivotally coupled to the forward portion of the first linkage and to the second linkage, wherein a front caster is connected to the third linkage; wherein the drive assembly is fixedly attached to the rearward portion of the first linkage; and wherein upward pivotal movement of the first and second linkages causes the third linkage to undergo upward movement and lateral movement toward the drive assembly.
 18. The wheelchair of claim 17 wherein the first linkage comprises a first length and the second linkage comprises a second length and wherein the first and second lengths are different.
 19. A wheelchair suspension comprising: a frame member having first and second sides; a first drive assembly coupled to said first side; a second drive assembly coupled to said second side; a first pivoting assembly coupled to said first side at a first pair of pivot axes; a second pivoting assembly coupled to said second side at a second pair of pivot axes; a front caster assembly coupled to each of the first and second pivoting assemblies, wherein each front caster assembly has a head tube rotatably receiving a caster fork that rotatably supports a caster wheel; wherein each of the first and second pivoting assemblies are configured such that upward movement of the front caster assembly relative to the frame causes the front caster wheel to move laterally toward the drive assembly; wherein a drive axle of a drive wheel of the first drive assembly is below said first pair of pivot axes when the wheelchair is disposed on a level support surface; and wherein a drive axle of a drive wheel of the second drive assembly is below said second pair of pivot axes when the wheelchair is disposed on a level support surface.
 20. The wheelchair suspension of claim 19 wherein the first and second drive assemblies are respectively coupled to the first and second pivoting assemblies. 